The present invention relates to a surveillance radar system and more particularly to a single radar system for not only determining azimuth and range of a target but also for finding the target height over limited range elevation angles
A two dimensional (2D) radar measures range and one angle coordinate (usually azimuth) It provides coverage over a volume and space extending from the radar site to the maximum detection range and from the horizon elevation up to the maximum target altitude of interest (usually 40,000 feet in the case of aircraft targets). The radar scans 360 degrees in azimuth with the antenna providing a complete rotation every five to ten seconds; as the antenna beam scans past the target, a number of pulse returns are received. These pulse returns are processed to eliminate returns from clutter and to integrate the target returns to make a detection decision on each target resulting in determining the target's azimuth and range.
Three dimensional (3D) radars measure, not only azimuth and range but also elevation angle or height above sea level. They are typically complex, expensive, heavy in antenna weight and have low S/N ratios due to fewer target pulse repetition frequency (PRF) returns. When elevation angle information is required the additional radar hardware is necessary. For a further discussion of 3D radar systems refer to "Introduction to Radar Systems" by Merrill I. Skolnik, second edition, 1980, pp. 541-547 and to U.S. Pat. No. 4,649,390 of LaVern A. Andrews et al. However, in certain applications such as air traffic control systems only limited heights are involved and a radar system not having the complexity of a typical 3D radar is desirable.
In U.S. Pat. No. 4,342,997 to Gary E. Evans, a radar antenna system is disclosed that adds height capability to a 2D array radar. A first subarray and a second subarray of antenna elements form two beams in different directions to achieve illumination characteristics of both the phase angle difference and the amplitude difference with respect to a common target for deriving the elevation of the target. However, this technique does require phase angle measurements in addition to amplitude measurements and includes parabolic cylinder reflector/linear array type antenna systems used in applications where a sharp underside cutoff region of long maximum range coverage is desireable; such a beam characteristic is generally not used for a terminal air traffic control application.